"Patrick" wrote in message
...
I have some vinatge headphones (Sennheiser HD424) and want to attach a new
plug.

Which color wires are the positive ones?

The colors in one of the leads are red & blue and in the other lead black &
yellow. (No wire is used as screening - there's just two wires in each
lead.)

Wire them up to a mono source and insert a dpdt switch so you can
easily and quickly reverse the phase of one earpiece. Insert a PVC
T coupling between the earpieces. Compare the sound levels coming
from the bottom of the T while flipping the switch. Loudest is in phase.
Art